(1) Field of the Invention
The present invention relates to high density silicon nitride sintered bodies having excellent mechanical strength, acidic resistance and static fatigue resistance, and to a method of manufacturing the same.
(2) Related Art Statement
Since silicin nitride sintered bodies have more excellent mechanical strength, heat resistance, heat shock resistance, and corrosion resistance than metallic materials, they have been examined for use in variety of mechanical parts which operate at such high temperatures where metallic materials usually fail, and uses of the silicon nitride sintered bodies have been actively developed. The materials to be used in the mechanical parts which are to operate at such high temperatures need to have excellent mechanical characteristics at high temperatures as well as high oxidation resistance and static fatigue resistance from the standpoint of the durability and dimensional stability during use of the parts for a long time period.
In order to obtain high density silicon nitride sintered bodies, there have been known a pressureless sintering process, a pressure sintering process, etc. Although various kinds of articles can easily inexpensively be mass-produced by the pressureless sintering process, this process has drawbacks in that an amount of a sintering aid necessary for obtaining high density is greater and the high temperature strength and oxidation resistance are insufficient. On the other hand, although higher density sintered bodies can be obtained with a lesser amount of a sintering aid by the pressure sintering process, it has a major drawback that production costs becomes extremely high in the case of mass production of large size articles having complicated shapes.
In order to solve the present above-mentioned problems, the inventors have proposed in Japanese patent application Laid-open No. 60-54,976 silicon nitride sintered bodies having high density, high strength and excellent oxidation resistance.
However, although the silicon nitride sintered bodies having high mechanical strength and oxidation resistance can be obtained in this method, silicon nitride sintered bodies which sufficiently a satisfy static fatigue characteristic, (SCG characteristic) which is important when in use as mechanical parts working particularly at high temperatures, cannot be obtained.